1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a semiconductor device having decreased mounting area in a printed circuit board and increasing efficiency of mounting thereof
2. Description of the Related Art
Semiconductor devices such as an integrated circuit (IC) or discrete transistor device are manufactured by using a mounting technology as shown in FIG. 1A. Numerical reference 1 denotes a silicon substrate or silicon semiconductor chip, 2 denotes an island for fixing the semiconductor chip 1, 3 denotes a lead terminal, 4 denotes a bonding wire, and 5 denotes a resin body for enclosing the semiconductor chip 1.
A semiconductor chip 1 having, for example, an NPN-type transistor structure is fixed on the island 2 by using an adhesive 6 such as solder. Lead terminals 3 are electrically connected to a base electrode and an emitter electrode of the semiconductor chip 1 respectively by bonding wire 4. The island 2 is electrically connected to a collector electrode of the semiconductor chip 1.
After the semiconductor chip 1 is mounted on the island 2, the semiconductor chip 1 and a portion of the lead terminal 3 are encased by transfer molding in the molded resin case, which is made of thermosetting resin such as epoxy resin or the like, such that a semiconductor device having a three terminal structure is provided. The lead terminals 3 extending out of the epoxy resin body 5 are bent into Z shapes.
In the manufacturing process of the semiconductor device, island 2 and lead terminals 3 are provided on a lead frame of hoop or rectangle shape, which is made of copper material or iron material. One lead frame has sets of islands 2 and lead terminals 3 corresponding to, for example, 20 semiconductor devices.
As shown in FIG. 1B, an upper metal mold 10 and lower metal mold 11 form a space therebetween which is a cavity 9, and which defines a shape of resin body 5 of the semiconductor device. In the cavity 9, the semiconductor chip 1 which is fixed on the island 2 of the lead frame with bonding wires 4 connected to the lead terminals 3, is set therein, and encased by thermosetting resin which is injected by transfer molding. Afterward, the lead terminals are cut away from the lead frame, and the encased chips on the lead frame are separated into individual devices.
First problem to be solved:
A resin molded semiconductor device (electrical component) is usually mounted on a printed-circuit board such as a glass-epoxy printed-circuit board, and is connected to other electrical components by wiring on the printed-circuit board, thereby providing a circuit network for performing a desired function. However, a conventional semiconductor device has lead terminals 3 protruding out of the resin body 5 by a length L as shown in FIG. 1A. The protruding portion L of the lead terminal needs excess space for mounting the resin body of the semiconductor device on the printed circuit board.
Second problem to be solved:
The transfer molding technology for encasing the semiconductor chip involves injecting thermosetting resin into a space (cavity) formed between the upper metal mold and the lower metal mold. Conventionally, one cavity is prepared for encasing one semiconductor chip, and each cavity has its path for injecting the thermosetting resin therethrough on the surfaces of the metal molds. Encasing is carried out by injection of the resin such that the resin is filled in the cavity and the path. Usually, epoxy resin which is used for encasing the semiconductor chip has thermosetting characteristics and utilization of wasted material is difficult. Therefore, the resin which is hardened and which remains in the path connected to the cavity is wasted and not to be utilized again for the products. The amount of the wasted resin is often larger than the amount of the resin utilized for the product, especially in the manufacturing process of smaller packages of the semiconductor devices. It is thus a drawback that the utilization efficiency of the thermosetting resin is poor.